Effect of Peripheral Substitution and Extended Conjugation on the Redox Potentials of Nickel Porphycenes

Eight different nickel porphycenes bearing substituents on the pyrrole β and/or ethylenic carbon positions of the macrocycle were investigated as to their redox properties in benzonitrile containing 0.1 M tetrabutylammonium perchlorate. Half-wave potentials were utilized to evaluate the effect of substituents and extended conjugation on the electrochemically measured HOMO−LUMO energy gap which is given by ΔE1/2 = E1/2(first oxidation) − E1/2(first reduction) and ranges between 1.33 and 2.01 V.